Conventionally, there has been disclosed an LED lighting device for supplying a power to an LED unit (see, e.g., Japanese Patent Application Publication No. 2006-210271 (JP2006-210271A), paragraphs [0031] to [0036] and FIG. 1). The LED lighting device includes a lighting circuit unit for converting a voltage inputted from a DC power supply to a predetermined DC voltage and outputting the DC voltage; a protection circuit unit for suppressing a rapid change in an output voltage in the lighting circuit unit; a voltage detecting circuit unit for detecting an output voltage from the lighting circuit unit; and a current detecting resistor for detecting a current flowing through the LED unit.
The lighting circuit unit includes an inductance element having a first terminal connected to a high-voltage port of the DC power supply; a backward current blocking diode having an anode connected to a second terminal of the inductance element; a switching element connected between the second terminal of the inductance element and a low-voltage port of the DC power supply; a capacitance element connected between a cathode of the backward current blocking diode and the low-voltage port of the DC power supply; and an operation controller for controlling an output voltage from the lighting circuit unit.
In this LED lighting device, the output voltage from the lighting circuit unit is adjusted such that a current flowing through the LED unit reaches a preset desired value, by allowing the operation controller to detect a current flowing through the LED unit by using the current detecting resistor and feeding back the detection result for on and off control of the switching element. Accordingly, even when the voltage of the DC power supply is varied, it is possible to keep the LED unit to have a uniform brightness.
When the LED lighting device disclosed in JP2006-210271A is operated, a current flowing through the inductance element becomes accumulated in the capacitance element. At this time, if a large current is supplied to the LED unit, the voltage of the capacitance element is smoothly increased. Moreover, in the case that an operating power of the operation controller is supplied from an output side of the lighting circuit unit, a control current from the operating power is also smoothly raised in proportion to the smooth increase in the voltage of the capacitance element. As a result, it would take time for the operating power of the operation controller to be stabilized.
Furthermore, when the control current from the operating power is designed to be steeply increased, a current supplied to the operation controller may be raised, thereby increasing power losses in the operating power or in the operation controller.